Japanese Patent Laying-Open No. 4-295202 discloses a motor drive capable of exchanging electric power between an AC power supply outside a vehicle and a DC power supply provided in the vehicle. The motor drive includes a battery, inverters IA and IB, induction motors MA and MB, and a control unit. Induction motors MA and MB include Y-connected windings CA and CB, respectively. To neutral points NA and NB of windings CA and CB, an input/output port is connected through an EMI filter. Inverters IA and IB are provided corresponding to induction motors MA and MB, respectively, and connected to windings CA and CB, respectively. Inverters IA and IB are connected parallel to the battery.
In the motor drive, in a recharge mode, an AC electric power applied from a single phase power supply connected to the input/output port across neutral points NA and NB of windings CA and CB can be converted to a DC electric power to charge the battery. Further, it is possible to generate an AC electric power having sinusoidal adjusted wave across neutral points NA and NB, and to output the generated AC electric power to an external device connected to the input/output port.
In the motor drive disclosed in Japanese Patent Laying-Open No. 4-295202 described above, however, driving of induction motors MA and MB must be stopped in the recharge mode. Further, while the induction motors MA and MB are controlled for driving (in the driving mode), recharge mode control is impossible.
Further, though the laid-open application discloses battery charge with power factor of 1 from a single phase power supply to realize efficient charging of a battery, control with higher accuracy is necessary to realize more efficient battery charge or power feed to an external device.